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<FONT color="green">001</FONT>    /*<a name="line.1"></a>
<FONT color="green">002</FONT>     * Licensed to the Apache Software Foundation (ASF) under one or more<a name="line.2"></a>
<FONT color="green">003</FONT>     * contributor license agreements.  See the NOTICE file distributed with<a name="line.3"></a>
<FONT color="green">004</FONT>     * this work for additional information regarding copyright ownership.<a name="line.4"></a>
<FONT color="green">005</FONT>     * The ASF licenses this file to You under the Apache License, Version 2.0<a name="line.5"></a>
<FONT color="green">006</FONT>     * (the "License"); you may not use this file except in compliance with<a name="line.6"></a>
<FONT color="green">007</FONT>     * the License.  You may obtain a copy of the License at<a name="line.7"></a>
<FONT color="green">008</FONT>     *<a name="line.8"></a>
<FONT color="green">009</FONT>     *      http://www.apache.org/licenses/LICENSE-2.0<a name="line.9"></a>
<FONT color="green">010</FONT>     *<a name="line.10"></a>
<FONT color="green">011</FONT>     * Unless required by applicable law or agreed to in writing, software<a name="line.11"></a>
<FONT color="green">012</FONT>     * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.12"></a>
<FONT color="green">013</FONT>     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.13"></a>
<FONT color="green">014</FONT>     * See the License for the specific language governing permissions and<a name="line.14"></a>
<FONT color="green">015</FONT>     * limitations under the License.<a name="line.15"></a>
<FONT color="green">016</FONT>     */<a name="line.16"></a>
<FONT color="green">017</FONT>    package org.apache.commons.lang3.concurrent;<a name="line.17"></a>
<FONT color="green">018</FONT>    <a name="line.18"></a>
<FONT color="green">019</FONT>    import java.util.concurrent.Callable;<a name="line.19"></a>
<FONT color="green">020</FONT>    import java.util.concurrent.ExecutionException;<a name="line.20"></a>
<FONT color="green">021</FONT>    import java.util.concurrent.ExecutorService;<a name="line.21"></a>
<FONT color="green">022</FONT>    import java.util.concurrent.Executors;<a name="line.22"></a>
<FONT color="green">023</FONT>    import java.util.concurrent.Future;<a name="line.23"></a>
<FONT color="green">024</FONT>    <a name="line.24"></a>
<FONT color="green">025</FONT>    /**<a name="line.25"></a>
<FONT color="green">026</FONT>     * &lt;p&gt;<a name="line.26"></a>
<FONT color="green">027</FONT>     * A class that allows complex initialization operations in a background task.<a name="line.27"></a>
<FONT color="green">028</FONT>     * &lt;/p&gt;<a name="line.28"></a>
<FONT color="green">029</FONT>     * &lt;p&gt;<a name="line.29"></a>
<FONT color="green">030</FONT>     * Applications often have to do some expensive initialization steps when they<a name="line.30"></a>
<FONT color="green">031</FONT>     * are started, e.g. constructing a connection to a database, reading a<a name="line.31"></a>
<FONT color="green">032</FONT>     * configuration file, etc. Doing these things in parallel can enhance<a name="line.32"></a>
<FONT color="green">033</FONT>     * performance as the CPU load can be improved. However, when access to the<a name="line.33"></a>
<FONT color="green">034</FONT>     * resources initialized in a background thread is actually required,<a name="line.34"></a>
<FONT color="green">035</FONT>     * synchronization has to be performed to ensure that their initialization is<a name="line.35"></a>
<FONT color="green">036</FONT>     * complete.<a name="line.36"></a>
<FONT color="green">037</FONT>     * &lt;/p&gt;<a name="line.37"></a>
<FONT color="green">038</FONT>     * &lt;p&gt;<a name="line.38"></a>
<FONT color="green">039</FONT>     * This abstract base class provides support for this use case. A concrete<a name="line.39"></a>
<FONT color="green">040</FONT>     * subclass must implement the {@link #initialize()} method. Here an arbitrary<a name="line.40"></a>
<FONT color="green">041</FONT>     * initialization can be implemented, and a result object can be returned. With<a name="line.41"></a>
<FONT color="green">042</FONT>     * this method in place the basic usage of this class is as follows (where<a name="line.42"></a>
<FONT color="green">043</FONT>     * {@code MyBackgroundInitializer} is a concrete subclass):<a name="line.43"></a>
<FONT color="green">044</FONT>     *<a name="line.44"></a>
<FONT color="green">045</FONT>     * &lt;pre&gt;<a name="line.45"></a>
<FONT color="green">046</FONT>     * MyBackgroundInitializer initializer = new MyBackgroundInitializer();<a name="line.46"></a>
<FONT color="green">047</FONT>     * initializer.start();<a name="line.47"></a>
<FONT color="green">048</FONT>     * // Now do some other things. Initialization runs in a parallel thread<a name="line.48"></a>
<FONT color="green">049</FONT>     * ...<a name="line.49"></a>
<FONT color="green">050</FONT>     * // Wait for the end of initialization and access the result object<a name="line.50"></a>
<FONT color="green">051</FONT>     * Object result = initializer.get();<a name="line.51"></a>
<FONT color="green">052</FONT>     * &lt;/pre&gt;<a name="line.52"></a>
<FONT color="green">053</FONT>     *<a name="line.53"></a>
<FONT color="green">054</FONT>     * &lt;/p&gt;<a name="line.54"></a>
<FONT color="green">055</FONT>     * &lt;p&gt;<a name="line.55"></a>
<FONT color="green">056</FONT>     * After the construction of a {@code BackgroundInitializer} object its<a name="line.56"></a>
<FONT color="green">057</FONT>     * {@link #start()} method has to be called. This starts the background<a name="line.57"></a>
<FONT color="green">058</FONT>     * processing. The application can now continue to do other things. When it<a name="line.58"></a>
<FONT color="green">059</FONT>     * needs access to the object produced by the {@code BackgroundInitializer} it<a name="line.59"></a>
<FONT color="green">060</FONT>     * calls its {@link #get()} method. If initialization is already complete,<a name="line.60"></a>
<FONT color="green">061</FONT>     * {@link #get()} returns the result object immediately. Otherwise it blocks<a name="line.61"></a>
<FONT color="green">062</FONT>     * until the result object is fully constructed.<a name="line.62"></a>
<FONT color="green">063</FONT>     * &lt;/p&gt;<a name="line.63"></a>
<FONT color="green">064</FONT>     * &lt;p&gt;<a name="line.64"></a>
<FONT color="green">065</FONT>     * {@code BackgroundInitializer} is a thin wrapper around a {@code Future}<a name="line.65"></a>
<FONT color="green">066</FONT>     * object and uses an {@code ExecutorService} for running the background<a name="line.66"></a>
<FONT color="green">067</FONT>     * initialization task. It is possible to pass in an {@code ExecutorService} at<a name="line.67"></a>
<FONT color="green">068</FONT>     * construction time or set one using {@code setExternalExecutor()} before<a name="line.68"></a>
<FONT color="green">069</FONT>     * {@code start()} was called. Then this object is used to spawn the background<a name="line.69"></a>
<FONT color="green">070</FONT>     * task. If no {@code ExecutorService} has been provided, {@code<a name="line.70"></a>
<FONT color="green">071</FONT>     * BackgroundInitializer} creates a temporary {@code ExecutorService} and<a name="line.71"></a>
<FONT color="green">072</FONT>     * destroys it when initialization is complete.<a name="line.72"></a>
<FONT color="green">073</FONT>     * &lt;/p&gt;<a name="line.73"></a>
<FONT color="green">074</FONT>     * &lt;p&gt;<a name="line.74"></a>
<FONT color="green">075</FONT>     * The methods provided by {@code BackgroundInitializer} provide for minimal<a name="line.75"></a>
<FONT color="green">076</FONT>     * interaction with the wrapped {@code Future} object. It is also possible to<a name="line.76"></a>
<FONT color="green">077</FONT>     * obtain the {@code Future} object directly. Then the enhanced functionality<a name="line.77"></a>
<FONT color="green">078</FONT>     * offered by {@code Future} can be used, e.g. to check whether the background<a name="line.78"></a>
<FONT color="green">079</FONT>     * operation is complete or to cancel the operation.<a name="line.79"></a>
<FONT color="green">080</FONT>     * &lt;/p&gt;<a name="line.80"></a>
<FONT color="green">081</FONT>     *<a name="line.81"></a>
<FONT color="green">082</FONT>     * @since 3.0<a name="line.82"></a>
<FONT color="green">083</FONT>     * @version $Id: BackgroundInitializer.java 1082044 2011-03-16 04:26:58Z bayard $<a name="line.83"></a>
<FONT color="green">084</FONT>     * @param &lt;T&gt; the type of the object managed by this initializer class<a name="line.84"></a>
<FONT color="green">085</FONT>     */<a name="line.85"></a>
<FONT color="green">086</FONT>    public abstract class BackgroundInitializer&lt;T&gt; implements<a name="line.86"></a>
<FONT color="green">087</FONT>            ConcurrentInitializer&lt;T&gt; {<a name="line.87"></a>
<FONT color="green">088</FONT>        /** The external executor service for executing tasks. */<a name="line.88"></a>
<FONT color="green">089</FONT>        private ExecutorService externalExecutor;<a name="line.89"></a>
<FONT color="green">090</FONT>    <a name="line.90"></a>
<FONT color="green">091</FONT>        /** A reference to the executor service that is actually used. */<a name="line.91"></a>
<FONT color="green">092</FONT>        private ExecutorService executor;<a name="line.92"></a>
<FONT color="green">093</FONT>    <a name="line.93"></a>
<FONT color="green">094</FONT>        /** Stores the handle to the background task. */<a name="line.94"></a>
<FONT color="green">095</FONT>        private Future&lt;T&gt; future;<a name="line.95"></a>
<FONT color="green">096</FONT>    <a name="line.96"></a>
<FONT color="green">097</FONT>        /**<a name="line.97"></a>
<FONT color="green">098</FONT>         * Creates a new instance of {@code BackgroundInitializer}. No external<a name="line.98"></a>
<FONT color="green">099</FONT>         * {@code ExecutorService} is used.<a name="line.99"></a>
<FONT color="green">100</FONT>         */<a name="line.100"></a>
<FONT color="green">101</FONT>        protected BackgroundInitializer() {<a name="line.101"></a>
<FONT color="green">102</FONT>            this(null);<a name="line.102"></a>
<FONT color="green">103</FONT>        }<a name="line.103"></a>
<FONT color="green">104</FONT>    <a name="line.104"></a>
<FONT color="green">105</FONT>        /**<a name="line.105"></a>
<FONT color="green">106</FONT>         * Creates a new instance of {@code BackgroundInitializer} and initializes<a name="line.106"></a>
<FONT color="green">107</FONT>         * it with the given {@code ExecutorService}. If the {@code ExecutorService}<a name="line.107"></a>
<FONT color="green">108</FONT>         * is not null, the background task for initializing this object will be<a name="line.108"></a>
<FONT color="green">109</FONT>         * scheduled at this service. Otherwise a new temporary {@code<a name="line.109"></a>
<FONT color="green">110</FONT>         * ExecutorService} is created.<a name="line.110"></a>
<FONT color="green">111</FONT>         *<a name="line.111"></a>
<FONT color="green">112</FONT>         * @param exec an external {@code ExecutorService} to be used for task<a name="line.112"></a>
<FONT color="green">113</FONT>         * execution<a name="line.113"></a>
<FONT color="green">114</FONT>         */<a name="line.114"></a>
<FONT color="green">115</FONT>        protected BackgroundInitializer(ExecutorService exec) {<a name="line.115"></a>
<FONT color="green">116</FONT>            setExternalExecutor(exec);<a name="line.116"></a>
<FONT color="green">117</FONT>        }<a name="line.117"></a>
<FONT color="green">118</FONT>    <a name="line.118"></a>
<FONT color="green">119</FONT>        /**<a name="line.119"></a>
<FONT color="green">120</FONT>         * Returns the external {@code ExecutorService} to be used by this class.<a name="line.120"></a>
<FONT color="green">121</FONT>         *<a name="line.121"></a>
<FONT color="green">122</FONT>         * @return the {@code ExecutorService}<a name="line.122"></a>
<FONT color="green">123</FONT>         */<a name="line.123"></a>
<FONT color="green">124</FONT>        public final synchronized ExecutorService getExternalExecutor() {<a name="line.124"></a>
<FONT color="green">125</FONT>            return externalExecutor;<a name="line.125"></a>
<FONT color="green">126</FONT>        }<a name="line.126"></a>
<FONT color="green">127</FONT>    <a name="line.127"></a>
<FONT color="green">128</FONT>        /**<a name="line.128"></a>
<FONT color="green">129</FONT>         * Returns a flag whether this {@code BackgroundInitializer} has already<a name="line.129"></a>
<FONT color="green">130</FONT>         * been started.<a name="line.130"></a>
<FONT color="green">131</FONT>         *<a name="line.131"></a>
<FONT color="green">132</FONT>         * @return a flag whether the {@link #start()} method has already been<a name="line.132"></a>
<FONT color="green">133</FONT>         * called<a name="line.133"></a>
<FONT color="green">134</FONT>         */<a name="line.134"></a>
<FONT color="green">135</FONT>        public synchronized boolean isStarted() {<a name="line.135"></a>
<FONT color="green">136</FONT>            return future != null;<a name="line.136"></a>
<FONT color="green">137</FONT>        }<a name="line.137"></a>
<FONT color="green">138</FONT>    <a name="line.138"></a>
<FONT color="green">139</FONT>        /**<a name="line.139"></a>
<FONT color="green">140</FONT>         * Sets an {@code ExecutorService} to be used by this class. The {@code<a name="line.140"></a>
<FONT color="green">141</FONT>         * ExecutorService} passed to this method is used for executing the<a name="line.141"></a>
<FONT color="green">142</FONT>         * background task. Thus it is possible to re-use an already existing<a name="line.142"></a>
<FONT color="green">143</FONT>         * {@code ExecutorService} or to use a specially configured one. If no<a name="line.143"></a>
<FONT color="green">144</FONT>         * {@code ExecutorService} is set, this instance creates a temporary one and<a name="line.144"></a>
<FONT color="green">145</FONT>         * destroys it after background initialization is complete. Note that this<a name="line.145"></a>
<FONT color="green">146</FONT>         * method must be called before {@link #start()}; otherwise an exception is<a name="line.146"></a>
<FONT color="green">147</FONT>         * thrown.<a name="line.147"></a>
<FONT color="green">148</FONT>         *<a name="line.148"></a>
<FONT color="green">149</FONT>         * @param externalExecutor the {@code ExecutorService} to be used<a name="line.149"></a>
<FONT color="green">150</FONT>         * @throws IllegalStateException if this initializer has already been<a name="line.150"></a>
<FONT color="green">151</FONT>         * started<a name="line.151"></a>
<FONT color="green">152</FONT>         */<a name="line.152"></a>
<FONT color="green">153</FONT>        public final synchronized void setExternalExecutor(<a name="line.153"></a>
<FONT color="green">154</FONT>                ExecutorService externalExecutor) {<a name="line.154"></a>
<FONT color="green">155</FONT>            if (isStarted()) {<a name="line.155"></a>
<FONT color="green">156</FONT>                throw new IllegalStateException(<a name="line.156"></a>
<FONT color="green">157</FONT>                        "Cannot set ExecutorService after start()!");<a name="line.157"></a>
<FONT color="green">158</FONT>            }<a name="line.158"></a>
<FONT color="green">159</FONT>    <a name="line.159"></a>
<FONT color="green">160</FONT>            this.externalExecutor = externalExecutor;<a name="line.160"></a>
<FONT color="green">161</FONT>        }<a name="line.161"></a>
<FONT color="green">162</FONT>    <a name="line.162"></a>
<FONT color="green">163</FONT>        /**<a name="line.163"></a>
<FONT color="green">164</FONT>         * Starts the background initialization. With this method the initializer<a name="line.164"></a>
<FONT color="green">165</FONT>         * becomes active and invokes the {@link #initialize()} method in a<a name="line.165"></a>
<FONT color="green">166</FONT>         * background task. A {@code BackgroundInitializer} can be started exactly<a name="line.166"></a>
<FONT color="green">167</FONT>         * once. The return value of this method determines whether the start was<a name="line.167"></a>
<FONT color="green">168</FONT>         * successful: only the first invocation of this method returns &lt;b&gt;true&lt;/b&gt;,<a name="line.168"></a>
<FONT color="green">169</FONT>         * following invocations will return &lt;b&gt;false&lt;/b&gt;.<a name="line.169"></a>
<FONT color="green">170</FONT>         *<a name="line.170"></a>
<FONT color="green">171</FONT>         * @return a flag whether the initializer could be started successfully<a name="line.171"></a>
<FONT color="green">172</FONT>         */<a name="line.172"></a>
<FONT color="green">173</FONT>        public synchronized boolean start() {<a name="line.173"></a>
<FONT color="green">174</FONT>            // Not yet started?<a name="line.174"></a>
<FONT color="green">175</FONT>            if (!isStarted()) {<a name="line.175"></a>
<FONT color="green">176</FONT>    <a name="line.176"></a>
<FONT color="green">177</FONT>                // Determine the executor to use and whether a temporary one has to<a name="line.177"></a>
<FONT color="green">178</FONT>                // be created<a name="line.178"></a>
<FONT color="green">179</FONT>                ExecutorService tempExec;<a name="line.179"></a>
<FONT color="green">180</FONT>                executor = getExternalExecutor();<a name="line.180"></a>
<FONT color="green">181</FONT>                if (executor == null) {<a name="line.181"></a>
<FONT color="green">182</FONT>                    executor = tempExec = createExecutor();<a name="line.182"></a>
<FONT color="green">183</FONT>                } else {<a name="line.183"></a>
<FONT color="green">184</FONT>                    tempExec = null;<a name="line.184"></a>
<FONT color="green">185</FONT>                }<a name="line.185"></a>
<FONT color="green">186</FONT>    <a name="line.186"></a>
<FONT color="green">187</FONT>                future = executor.submit(createTask(tempExec));<a name="line.187"></a>
<FONT color="green">188</FONT>    <a name="line.188"></a>
<FONT color="green">189</FONT>                return true;<a name="line.189"></a>
<FONT color="green">190</FONT>            }<a name="line.190"></a>
<FONT color="green">191</FONT>    <a name="line.191"></a>
<FONT color="green">192</FONT>            return false;<a name="line.192"></a>
<FONT color="green">193</FONT>        }<a name="line.193"></a>
<FONT color="green">194</FONT>    <a name="line.194"></a>
<FONT color="green">195</FONT>        /**<a name="line.195"></a>
<FONT color="green">196</FONT>         * Returns the result of the background initialization. This method blocks<a name="line.196"></a>
<FONT color="green">197</FONT>         * until initialization is complete. If the background processing caused a<a name="line.197"></a>
<FONT color="green">198</FONT>         * runtime exception, it is directly thrown by this method. Checked<a name="line.198"></a>
<FONT color="green">199</FONT>         * exceptions, including {@code InterruptedException} are wrapped in a<a name="line.199"></a>
<FONT color="green">200</FONT>         * {@link ConcurrentException}. Calling this method before {@link #start()}<a name="line.200"></a>
<FONT color="green">201</FONT>         * was called causes an {@code IllegalStateException} exception to be<a name="line.201"></a>
<FONT color="green">202</FONT>         * thrown.<a name="line.202"></a>
<FONT color="green">203</FONT>         *<a name="line.203"></a>
<FONT color="green">204</FONT>         * @return the object produced by this initializer<a name="line.204"></a>
<FONT color="green">205</FONT>         * @throws ConcurrentException if a checked exception occurred during<a name="line.205"></a>
<FONT color="green">206</FONT>         * background processing<a name="line.206"></a>
<FONT color="green">207</FONT>         * @throws IllegalStateException if {@link #start()} has not been called<a name="line.207"></a>
<FONT color="green">208</FONT>         */<a name="line.208"></a>
<FONT color="green">209</FONT>        public T get() throws ConcurrentException {<a name="line.209"></a>
<FONT color="green">210</FONT>            try {<a name="line.210"></a>
<FONT color="green">211</FONT>                return getFuture().get();<a name="line.211"></a>
<FONT color="green">212</FONT>            } catch (ExecutionException execex) {<a name="line.212"></a>
<FONT color="green">213</FONT>                ConcurrentUtils.handleCause(execex);<a name="line.213"></a>
<FONT color="green">214</FONT>                return null; // should not be reached<a name="line.214"></a>
<FONT color="green">215</FONT>            } catch (InterruptedException iex) {<a name="line.215"></a>
<FONT color="green">216</FONT>                // reset interrupted state<a name="line.216"></a>
<FONT color="green">217</FONT>                Thread.currentThread().interrupt();<a name="line.217"></a>
<FONT color="green">218</FONT>                throw new ConcurrentException(iex);<a name="line.218"></a>
<FONT color="green">219</FONT>            }<a name="line.219"></a>
<FONT color="green">220</FONT>        }<a name="line.220"></a>
<FONT color="green">221</FONT>    <a name="line.221"></a>
<FONT color="green">222</FONT>        /**<a name="line.222"></a>
<FONT color="green">223</FONT>         * Returns the {@code Future} object that was created when {@link #start()}<a name="line.223"></a>
<FONT color="green">224</FONT>         * was called. Therefore this method can only be called after {@code<a name="line.224"></a>
<FONT color="green">225</FONT>         * start()}.<a name="line.225"></a>
<FONT color="green">226</FONT>         *<a name="line.226"></a>
<FONT color="green">227</FONT>         * @return the {@code Future} object wrapped by this initializer<a name="line.227"></a>
<FONT color="green">228</FONT>         * @throws IllegalStateException if {@link #start()} has not been called<a name="line.228"></a>
<FONT color="green">229</FONT>         */<a name="line.229"></a>
<FONT color="green">230</FONT>        public synchronized Future&lt;T&gt; getFuture() {<a name="line.230"></a>
<FONT color="green">231</FONT>            if (future == null) {<a name="line.231"></a>
<FONT color="green">232</FONT>                throw new IllegalStateException("start() must be called first!");<a name="line.232"></a>
<FONT color="green">233</FONT>            }<a name="line.233"></a>
<FONT color="green">234</FONT>    <a name="line.234"></a>
<FONT color="green">235</FONT>            return future;<a name="line.235"></a>
<FONT color="green">236</FONT>        }<a name="line.236"></a>
<FONT color="green">237</FONT>    <a name="line.237"></a>
<FONT color="green">238</FONT>        /**<a name="line.238"></a>
<FONT color="green">239</FONT>         * Returns the {@code ExecutorService} that is actually used for executing<a name="line.239"></a>
<FONT color="green">240</FONT>         * the background task. This method can be called after {@link #start()}<a name="line.240"></a>
<FONT color="green">241</FONT>         * (before {@code start()} it returns &lt;b&gt;null&lt;/b&gt;). If an external executor<a name="line.241"></a>
<FONT color="green">242</FONT>         * was set, this is also the active executor. Otherwise this method returns<a name="line.242"></a>
<FONT color="green">243</FONT>         * the temporary executor that was created by this object.<a name="line.243"></a>
<FONT color="green">244</FONT>         *<a name="line.244"></a>
<FONT color="green">245</FONT>         * @return the {@code ExecutorService} for executing the background task<a name="line.245"></a>
<FONT color="green">246</FONT>         */<a name="line.246"></a>
<FONT color="green">247</FONT>        protected synchronized final ExecutorService getActiveExecutor() {<a name="line.247"></a>
<FONT color="green">248</FONT>            return executor;<a name="line.248"></a>
<FONT color="green">249</FONT>        }<a name="line.249"></a>
<FONT color="green">250</FONT>    <a name="line.250"></a>
<FONT color="green">251</FONT>        /**<a name="line.251"></a>
<FONT color="green">252</FONT>         * Returns the number of background tasks to be created for this<a name="line.252"></a>
<FONT color="green">253</FONT>         * initializer. This information is evaluated when a temporary {@code<a name="line.253"></a>
<FONT color="green">254</FONT>         * ExecutorService} is created. This base implementation returns 1. Derived<a name="line.254"></a>
<FONT color="green">255</FONT>         * classes that do more complex background processing can override it. This<a name="line.255"></a>
<FONT color="green">256</FONT>         * method is called from a synchronized block by the {@link #start()}<a name="line.256"></a>
<FONT color="green">257</FONT>         * method. Therefore overriding methods should be careful with obtaining<a name="line.257"></a>
<FONT color="green">258</FONT>         * other locks and return as fast as possible.<a name="line.258"></a>
<FONT color="green">259</FONT>         *<a name="line.259"></a>
<FONT color="green">260</FONT>         * @return the number of background tasks required by this initializer<a name="line.260"></a>
<FONT color="green">261</FONT>         */<a name="line.261"></a>
<FONT color="green">262</FONT>        protected int getTaskCount() {<a name="line.262"></a>
<FONT color="green">263</FONT>            return 1;<a name="line.263"></a>
<FONT color="green">264</FONT>        }<a name="line.264"></a>
<FONT color="green">265</FONT>    <a name="line.265"></a>
<FONT color="green">266</FONT>        /**<a name="line.266"></a>
<FONT color="green">267</FONT>         * Performs the initialization. This method is called in a background task<a name="line.267"></a>
<FONT color="green">268</FONT>         * when this {@code BackgroundInitializer} is started. It must be<a name="line.268"></a>
<FONT color="green">269</FONT>         * implemented by a concrete subclass. An implementation is free to perform<a name="line.269"></a>
<FONT color="green">270</FONT>         * arbitrary initialization. The object returned by this method can be<a name="line.270"></a>
<FONT color="green">271</FONT>         * queried using the {@link #get()} method.<a name="line.271"></a>
<FONT color="green">272</FONT>         *<a name="line.272"></a>
<FONT color="green">273</FONT>         * @return a result object<a name="line.273"></a>
<FONT color="green">274</FONT>         * @throws Exception if an error occurs<a name="line.274"></a>
<FONT color="green">275</FONT>         */<a name="line.275"></a>
<FONT color="green">276</FONT>        protected abstract T initialize() throws Exception;<a name="line.276"></a>
<FONT color="green">277</FONT>    <a name="line.277"></a>
<FONT color="green">278</FONT>        /**<a name="line.278"></a>
<FONT color="green">279</FONT>         * Creates a task for the background initialization. The {@code Callable}<a name="line.279"></a>
<FONT color="green">280</FONT>         * object returned by this method is passed to the {@code ExecutorService}.<a name="line.280"></a>
<FONT color="green">281</FONT>         * This implementation returns a task that invokes the {@link #initialize()}<a name="line.281"></a>
<FONT color="green">282</FONT>         * method. If a temporary {@code ExecutorService} is used, it is destroyed<a name="line.282"></a>
<FONT color="green">283</FONT>         * at the end of the task.<a name="line.283"></a>
<FONT color="green">284</FONT>         *<a name="line.284"></a>
<FONT color="green">285</FONT>         * @param execDestroy the {@code ExecutorService} to be destroyed by the<a name="line.285"></a>
<FONT color="green">286</FONT>         * task<a name="line.286"></a>
<FONT color="green">287</FONT>         * @return a task for the background initialization<a name="line.287"></a>
<FONT color="green">288</FONT>         */<a name="line.288"></a>
<FONT color="green">289</FONT>        private Callable&lt;T&gt; createTask(ExecutorService execDestroy) {<a name="line.289"></a>
<FONT color="green">290</FONT>            return new InitializationTask(execDestroy);<a name="line.290"></a>
<FONT color="green">291</FONT>        }<a name="line.291"></a>
<FONT color="green">292</FONT>    <a name="line.292"></a>
<FONT color="green">293</FONT>        /**<a name="line.293"></a>
<FONT color="green">294</FONT>         * Creates the {@code ExecutorService} to be used. This method is called if<a name="line.294"></a>
<FONT color="green">295</FONT>         * no {@code ExecutorService} was provided at construction time.<a name="line.295"></a>
<FONT color="green">296</FONT>         *<a name="line.296"></a>
<FONT color="green">297</FONT>         * @return the {@code ExecutorService} to be used<a name="line.297"></a>
<FONT color="green">298</FONT>         */<a name="line.298"></a>
<FONT color="green">299</FONT>        private ExecutorService createExecutor() {<a name="line.299"></a>
<FONT color="green">300</FONT>            return Executors.newFixedThreadPool(getTaskCount());<a name="line.300"></a>
<FONT color="green">301</FONT>        }<a name="line.301"></a>
<FONT color="green">302</FONT>    <a name="line.302"></a>
<FONT color="green">303</FONT>        private class InitializationTask implements Callable&lt;T&gt; {<a name="line.303"></a>
<FONT color="green">304</FONT>            /** Stores the executor service to be destroyed at the end. */<a name="line.304"></a>
<FONT color="green">305</FONT>            private final ExecutorService execFinally;<a name="line.305"></a>
<FONT color="green">306</FONT>    <a name="line.306"></a>
<FONT color="green">307</FONT>            /**<a name="line.307"></a>
<FONT color="green">308</FONT>             * Creates a new instance of {@code InitializationTask} and initializes<a name="line.308"></a>
<FONT color="green">309</FONT>             * it with the {@code ExecutorService} to be destroyed at the end.<a name="line.309"></a>
<FONT color="green">310</FONT>             *<a name="line.310"></a>
<FONT color="green">311</FONT>             * @param exec the {@code ExecutorService}<a name="line.311"></a>
<FONT color="green">312</FONT>             */<a name="line.312"></a>
<FONT color="green">313</FONT>            public InitializationTask(ExecutorService exec) {<a name="line.313"></a>
<FONT color="green">314</FONT>                execFinally = exec;<a name="line.314"></a>
<FONT color="green">315</FONT>            }<a name="line.315"></a>
<FONT color="green">316</FONT>    <a name="line.316"></a>
<FONT color="green">317</FONT>            /**<a name="line.317"></a>
<FONT color="green">318</FONT>             * Initiates initialization and returns the result.<a name="line.318"></a>
<FONT color="green">319</FONT>             *<a name="line.319"></a>
<FONT color="green">320</FONT>             * @return the result object<a name="line.320"></a>
<FONT color="green">321</FONT>             * @throws Exception if an error occurs<a name="line.321"></a>
<FONT color="green">322</FONT>             */<a name="line.322"></a>
<FONT color="green">323</FONT>            public T call() throws Exception {<a name="line.323"></a>
<FONT color="green">324</FONT>                try {<a name="line.324"></a>
<FONT color="green">325</FONT>                    return initialize();<a name="line.325"></a>
<FONT color="green">326</FONT>                } finally {<a name="line.326"></a>
<FONT color="green">327</FONT>                    if (execFinally != null) {<a name="line.327"></a>
<FONT color="green">328</FONT>                        execFinally.shutdown();<a name="line.328"></a>
<FONT color="green">329</FONT>                    }<a name="line.329"></a>
<FONT color="green">330</FONT>                }<a name="line.330"></a>
<FONT color="green">331</FONT>            }<a name="line.331"></a>
<FONT color="green">332</FONT>        }<a name="line.332"></a>
<FONT color="green">333</FONT>    }<a name="line.333"></a>




























































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